Two-dimensional position sensor

ABSTRACT

A capacitive position sensor comprises a substrate having an arrangement of electrodes mounted on a single surface thereof, the electrodes arranged so as to define an array of sensing cells arranged in columns and rows to form a sensing area. Each sensing cell includes a column sensing electrode and a row sensing electrode. The column sensing electrodes of sensing cells in the same column are electrically coupled together, and the row sensing electrodes of sensing cells in the same row are electrically coupled together. Row sensing electrodes of sensing cells at opposing ends of at least one of the rows are connected together by an electrical connection made outside of the sensing area so that there is no requirement for electrical connections to cross within the sensing area, providing a capacitive position sensor having a sensing area with electrodes on only one side of a substrate.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/899,353 filed 6 Oct. 2010, which is a continuation of U.S.application Ser. No. 11/428,670 filed 5 Jul. 2006, now U.S. Pat. No.7,821,502 issued 26 Oct. 2010, which claims priority to U.S. ProvisionalApplication No. 60/697,613 filed 8 Jul. 2005.

BACKGROUND OF THE INVENTION

The invention relates to a capacitive position sensor for determiningthe position of an object within a two-dimensional sensing area.

The use of two-dimensional touch-sensitive position sensors is becomingmore common. Examples include the use of position sensors in laptopcomputers in place of mouse pointing devices, as control panels forreceiving user inputs to control an appliance, or particularly as aglass touchscreen apparatus having an X-Y coordinate output. Someapplications require a clear sensing layer so that a display can beviewed beneath the screen, while others only require an opaque touchsurface, for example for a keypanel on a kitchen appliance or a PCperipheral.

Touch-sensitive position sensors are frequently preferred to mechanicaldevices because they provide for a more robust interface and are oftenconsidered to be more aesthetically pleasing. Furthermore, becausetouch-sensitive position sensors require no moving parts to beaccessible to a user, they are less prone to wear than their mechanicalcounterparts and can be provided within a sealed outer surface. Thismakes their use where there is a danger of dirt or fluids entering adevice being controlled particularly attractive.

There exists a large body of art involving 2D touchpanels and screens.They can be generally divided into two classifications: those thatreport an X-Y coordinate of a more or less continuous nature (‘XY’type), and those that have a discrete sensing surface (‘discrete’ type)having predefined key areas that are fixed by physical geometry. The XYtype find dominant use over LCD or other display types while the latterfind use in fixed function key panels. There are exceptions to this, forexample touchpad surfaces on laptops report XY position but are opaque.XY types invariably involve a sensing surface on the user-side or ‘firstsurface’ of the touch area. For example, both continuous resistive andcapacitive touch screens involve a sensing layer that must be eitherphysically depressed by the user or touched almost directly, or at mostthrough a thin layer of insulation (as in mouse touchpads). These typesrequire that the product have a bezel opening to allow direct ornear-direct contact by the user with the sensing layer. A significantdisadvantage of these types is that there has to be an opening in thepanel, which requires sealing against moisture and dirt and hence isexpensive to mount. Furthermore the sensing layer is directly exposed toabuse and can be easily damaged by sharp objects or abrasion. Whilerobust capacitive types are known which have buried wires inside a glasslayer (e.g. U.S. Pat. No. 5,844,506), these still require a bezelopening in a panel which must be sealed, and require two sensing layersas a matrix due to the need to cross X and Y conductors. Furthermorethese screens are very expensive to produce and in fact cannot beproduced on a mass scale; additionally the sensing circuitry is known tobe complex and expensive.

In the field of discrete touch buttons, it has been known for some timethat capacitive keys can be placed behind a solid surface having norequirement for a bezel opening. However these types only provide forlimited resolution, as predefined by the location of discrete electrodeshapes. An example of this can be found in U.S. Pat. No. 4,954,823,FIGS. 4 and 6. While it is well known that these electrodes can be madeof a single layer of clear conductor such as Indium Tin Oxide (‘ITO’) toallow placement over a bezel-less display, for example by theapplication of the layer as a film on the back of a subsection of apanel, nevertheless the technology is limited to discrete touch areasbased on the number, size, and placement of discrete electrodes.

FIG. 1 schematically shows in plan view a touch pad 2 of the typedescribed in U.S. Pat. No. 4,954,823, but laid out in an orthogonalarray. The touch pad 2 comprises a grid of discrete electrodes 4 mountedon an insulating substrate 6. Each electrode is connected to a channelof capacitance measurement circuitry in a controller 8. U.S. Pat. No.5,463,388 describes this geometry in passing in conjunction with itsFIG. 1, to show how such an array can be used to determine a position ofan object proximate the sensing layer via a method of determining acentroid of the signals from each pad. However U.S. Pat. No. 5,463,388fails to show how to implement such a design and describes instead amatrix of conductors along with a centroidal calculation of continuousX-Y position. In fact it is not practical to have so many sensingchannels as one per sense pad, and a matrix arrangement is much moreefficient as described below.

FIG. 2 schematically shows a position sensor 12 based on a matrix ofconductors as described in U.S. Pat. No. 5,463,388. The position sensor12 comprises a number of vertically aligned strip electrodes (columns)14 mounted on an upper surface of an insulating substrate 16 and anumber of horizontally aligned strip electrodes (rows) 15 mounted on anopposing lower surface of the insulating substrate. Each vertical stripelectrode is connected to a channel of capacitance measurement circuitryin a controller 18. Thus, this type of position sensor allows an X-Ycoordinate output of a continuous nature by means of calculation of acentroid of capacitance among the rows and columns rather than amongdiscrete pads. However this type requires two sensing layers so that thematrix traces can be routed, and does not allow the use of opticallyclear materials.

The ideal touch surface would eliminate the need for a bezel opening (orat least, make it optional), have an inexpensive sensing surface that isapplied to the rear of the panel surface that can project through areasonable thickness of panel material (e.g. up to 4 mm of glass orplastic), optionally require only one sensing layer with no crossoversin the sensing region, be usable with clear sensing layers such as ITO,have an XY type of output, and have a compact, inexpensive drivercircuit. This set of ideal goals has not been achieved with any knownprior art.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided acapacitive position sensor for determining the position of an object ina sensing area, the sensor comprising a substrate having a surface withan arrangement of electrodes mounted thereon, wherein the electrodesdefine an array of sensing cells arranged in columns and rows to formthe sensing area, each sensing cell including a column sensing electrodeand a row sensing electrode, the column sensing electrodes of sensingcells in the same column being electrically coupled together and the rowsensing electrodes of sensing cells in the same row being electricallycoupled together, wherein row sensing electrodes of sensing cells atopposing ends of at least one of the rows are electrically coupled toone another by respective row wrap-around connections made outside ofthe sensing area.

Thus a position sensor having electrodes on only a single layer of asubstrate can be provided. Furthermore, because the position sensoremploys an intersecting array of columns and rows of sensing electrodes(i.e. a matrix), fewer measurement channels are required than withsensors based on an array of discrete electrodes.

Because the position sensor is based on sensing electrodes on only asingle surface, it can be cheaper to manufacture than known double-sidedposition sensors. This also means the sensing electrodes can bedeposited directly onto a surface for which the opposing surface isinaccessible (e.g. a display screen). The sensing electrodes can also bedeposited on an inside surface of a device housing, thus removing theneed for any protective covering that might be required if electrodeswere also required to be on the outer surface.

The electrical row wrap-around connections may comprise a conductivetrace mounted on the substrate. This allows the connection outside ofthe sensing area to be made in the same processing step as the sensingelectrodes within it. Alternatively, the row wrap-around connections maybe made by a free wire appropriately connected to the respective rowsensing electrodes.

The column sensing electrodes of a column of sensing cells at an edge ofthe sensing area may be electrically coupled to one another by columnwrap-around connections made outside of the sensing area in a similarfashion.

The position sensor may further comprise a plurality of capacitancemeasurement channels connected to respective ones of the rows of rowsensing electrodes and the columns of column sensing electrodes, whereineach measurement channel is operable to generate a signal indicative ofa capacitance between its associated column or row of sensing electrodesand a system ground.

In addition, the position sensor may further comprise a processoroperable to determine the position of the object along the firstdirection by comparing signals from the columns of column sensingelectrodes and along the second direction by comparing signals from therows of row sensing electrodes.

This allows the determination of the position of a touch to be madeusing otherwise conventional circuitry connected to the sensingelements.

The capacitance measurement channels may comprise charge transfercircuitry since this provides a reliable and robust way to measurecapacitances of the level that might be expected in a typicalimplementation. However, other forms of capacitance measurementcircuitry may equally be used. In general it is preferential to use acapacitive driver circuit that drives all the rows and columnconnections in a substantially phase-synchronous manner so as to preventthe electric fields from cross-loading into adjacent rows and columns.This is described also in U.S. Pat. No. 5,463,388, where all the rowsand column conductors are driven by a single oscillator.

The sensing cells may be arranged into three or four columns. This canprovide a position sensor with sufficient resolution over a typicallysized sensing area for most applications.

The column and row sensing electrodes in each sensing cell may beinterleaved with one another (e.g. by spiraling around one another orbeing interlaced/intertwined), especially in designs where the row andcolumn spacing is larger than that of a typical finger. This providesfor a much more uniform blend of signals from the X and Y drives in eachintersecting location, allowing better position reporting with respectto a finger touching the overlying surface. This is described also inU.S. Pat. No. 5,463,388, for example FIG. 2. In layouts where the rowand column spacings are similar to or smaller than a human finger it issufficient to use other arrangements of electrode pattern, for examplean array of diamond shapes as shown in FIG. 8 and described furtherbelow.

The position sensor may include a transparent substrate and transparentelectrodes (e.g. formed from Indium Tin Oxide (ITO) deposited on thesubstrate). This allows it to be placed over a display screen withoutobscuring what is displayed beneath. Thus the display screen might beconfigured to display “virtual” buttons to a user that may be selectedby the user placing their finger over the appropriate part of thedisplay adjacent the position sensor. The position of the user's touchcan then be compared with the positions of the “virtual” buttons beingdisplayed to determine which one has been selected.

According to a second aspect of the invention there is provided a devicecomprising a position sensor according to the first aspect of theinvention. The position sensor may be used in many types of device. Forexample the device may be a portable/hand-held device, e.g. a personaldata assistant (PDA), a multimedia player, a mobile (cell) phone, are-configurable remote controller, or a still camera or video camera,for example with the position sensor overlaying a display.Alternatively, the position sensor could equally be used in larger scaledevices such as kitchen appliances, kiosks, and the like. Opaqueversions can be fashioned for use in PC-style trackpads, keypads, andother human interface devices as are well known in the art.

According to a third aspect of the invention there is provided a methodof constructing a capacitively sensitive surface disposed on a substratewhich reports an X-Y coordinate position of an object within an activesensing region when the object is adjacent to said surface, comprisingthe steps of: (a) depositing a single layer of patterned conductivematerial in the active sensing region, the pattern comprising rows andcolumns of electrodes connected to individual ones of capacitive sensingchannels, and wherein at least one row or column is broken into aplurality of segments within the active region; (b) connecting thebroken segments together with an electrical conductor, wherein theconductor is made to lie outside of the active sensing region; (c)connecting the rows and columns to individual sensing channels of amulti-channel capacitive sensor circuit having multiple outputsrepresenting amplitudes of capacitance on the rows and columns; and (d)providing a processor operable to process the multiple outputs todetermine a coordinate position of the adjacent object as an XYlocation.

The processor may be operable to compensate for position distortionintroduced by the physical geometry of the patterned conductivematerial.

The processor may also be operable to calculate a centroid of thesignals across rows and a centroid of the signals across columns.

According to a fourth aspect of the invention there is provided acapacitive position sensor for determining the position of an object ina sensing area, the sensor comprising a substrate having a surface withan arrangement of conductive electrodes mounted thereon, wherein theelectrodes define an array of sensing cells arranged in columns and rowsto form the sensing area, each sensing cell including a column sensingelectrode and a row sensing electrode, the column sensing electrodes ofsensing cells in the same column being electrically coupled together andthe row sensing electrodes of sensing cells in the same row beingelectrically coupled together, wherein at least one column sensingelectrode comprises a continuous spine within the sensing area, and theat least one other column is made electrically continuous viaconnections external to the sensing area.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same maybe carried into effect reference is now made by way of example to theaccompanying drawings in which:

FIG. 1 schematically shows in plan view a known two-dimensionalcapacitive position sensor;

FIG. 2 schematically shows in plan view another known two-dimensionalcapacitive position sensor;

FIG. 3 schematically shows in plan view a two-dimensional capacitiveposition sensor according to an embodiment of the invention;

FIG. 4 schematically shows in perspective view a device including theposition sensor of FIG. 3;

FIGS. 5A and 5B are graphs schematically showing capacitance as functionof column number (FIG. 5A) and row number (FIG. 5B) of sensing cellsused to determine the position of an object adjacent the position sensorof the device shown in FIG. 4;

FIG. 6 schematically shows in plan view the two-dimensional capacitiveposition sensor and display screen of the device shown in FIG. 4;

FIGS. 7 and 8 schematically show in plan view two-dimensional capacitiveposition sensors according to other embodiments of the invention;

FIG. 9 schematically shows in plan view reported positions compared toactual positions for an object adjacent a position sensor according toan embodiment of the invention; and

FIG. 10 schematically shows in plan view a display of the outlines ofdesired key positions compared to the outlines of reported key positionsfor a position sensor according to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 3 schematically shows in plan view a two-dimensionaltouch-sensitive capacitive position sensor 22 according to an embodimentof the invention. The position sensor 22 is operable to determine theposition of an object along a first (x) and a second (y) direction, theorientation of which are shown towards the top left of the drawing. Thesensor 22 comprises a substrate 24 having an arrangement of sensingelectrodes 26 mounted thereon. The sensing electrodes 26 define asensing area within which the position of an object (e.g. a finger orstylus) adjacent the sensor may be determined. The substrate 24 is of atransparent plastics material and the electrodes are formed from atransparent film of Indium Tin Oxide (ITO) deposited on the substrate 24using conventional techniques. Thus the sensing area of the sensor istransparent and can be placed over a display screen without obscuringwhat is displayed behind the sensing area. In other examples theposition sensor may not be intended to be located over a display and maynot be transparent; in these instances the ITO layer may be replacedwith a more economical material such as a copper laminate PCB, forexample.

The pattern of the sensing electrodes on the substrate 24 is such as todivide the sensing area into an array (grid) of sensing cells 28arranged into rows and columns. (It is noted that the terms “row” and“column” are used here to conveniently distinguish between twodirections and should not be interpreted to imply either a vertical or ahorizontal orientation.) By way of example one of the sensing cell 28 isidentified by a dotted outline in FIG. 3. In this position sensor thereare four columns of sensing cells aligned with the y-direction and fiverows of sensing cells aligned with the x direction (twenty sensing cellsin total). The top-most row of sensing cells for the orientation shownin FIG. 3 is referred to as row y1, the next one down as row y2, and soon down to row y5. The columns of sensing cells are similarly referredto from left to right as columns x1 to x4. Thus the sensing cell 28shown with a dotted outline in FIG. 3 is at the intersection of row y1and column x3.

Each sensing cell includes a row sensing electrode 30 and a columnsensing electrode 32. The row sensing electrodes 30 and column sensingelectrodes are arranged within each sensing cell 28 to interleave withone another (in this case by squared spiraling around one another), butare not galvanically connected. Because the row and column sensingelectrodes are interleaved (intertwined), an object adjacent a givensensing cell can provide a significant capacitive coupling to bothsensing electrodes irrespective of where in the sensing cell the objectis positioned. The characteristic scale of interleaving may be on theorder of, or smaller than, the capacitive footprint of a typical objectto be detected to provide the best results. The size and shape of thesensing cell 28 can be comparable to that of the object to be detectedor larger (within practical limits).

The row sensing electrodes 30 of all sensing cells in the same row areelectrically connected together to form five separate rows of rowsensing electrodes. Similarly, the column sensing electrodes 32 of allsensing cells in the same column are electrically connected together toform four separate columns of column sensing electrodes.

The column sensing electrodes in column x2 are connected to one anotherby a connection 51, also referred to as a spine, made within the sensingarea by a part of one of the electrodes deposited on the substrate andwhich runs between columns x2 and x3. This connection runs the length ofthe sensing area. Thus a single continuous conductive electrodedeposited on the substrate 24 provides the column sensing electrodes 32of all of the sensing cells in column x2 and their interconnections. Thecolumn sensing electrodes in column x3 are similarly connected to oneanother by a connection 53 made within the sensing area, again runningbetween columns x2 and x3 as a spine. Thus again a single continuousconductive electrode deposited in the substrate 24 provides the columnsensing electrodes 32 of all of the sensing cells in column x3 and theirinterconnections.

The row sensing electrodes 30 in columns x1 and x2 of row y2 are alsoconnected together by a connection made within the sensing area. Thus asingle continuous conductive electrode 34 deposited on the substrate 24provides the row sensing electrodes of the sensing cells in columns x1and x2 of row y2 and their interconnection. The row sensing electrodesin columns x3 and x4 of row y2 are similarly connected together by aconnection made within the sensing area so that a single continuouselectrode 36 again provides these row sensing electrodes and theirinterconnection. However, because of the on-substrate connections(spines) running between columns x2 and x3 to connect between theirrespective column sensing electrodes, the row sensing electrodes incolumns x1 and x2 of row y2 cannot be connected to the row sensingelectrodes in columns x3 and x4 of row y2 by a connection made on thesurface of the substrate. Thus a connection 38 between the row sensingelectrodes at opposing ends of this row (i.e. in columns x1 and x4) isprovided outside of the sensing area. The connection 38 runs around theoutside of the sensing area to connect the electrode 34 providing therow sensing electrodes in columns x1 and x2 of row y2 with the electrode36 providing the row sensing electrodes in columns x3 and x4 of row y2.Thus all row sensing electrodes in this row are electrically connectedtogether. Similar wrap-around connections outside of the sensing areaare made to ensure the respective row sensing electrodes of the otherrows are connected together. It is noted that although one is shown inFIG. 3, a connection outside of the sensing area between the row sensingelectrodes at opposing ends of row y1 is not required because the spinesconnecting between the column sensing electrodes of columns x2 and x3need not extend to the very edge of the sensing area and a connectionrunning along the top edge of the sensing area could be used to connectbetween the row sensing electrodes in row y1 (not shown).

Each column sensing electrode in column x1 is formed from a separateelectrode on the substrate. These separate electrodes are connectedtogether by connections 40 made external to (i.e. outside of) thesensing area. The column sensing electrodes in column x4 are connectedtogether by connections 41 in a similar manner to those of column x1. Inthis fashion the outer two columns can be discontinuous within thesensing area to allow access by row electrodes into cells, yet thecolumns are nevertheless made whole.

In this example the various connections made outside of the sensing areabetween the row sensing electrodes in sensing cells at opposing ends ofthe respective rows and the column sensing electrodes in the columns atthe periphery of the sensing area are formed from free wires attached tothe electrodes of the sensing area as appropriate using conventionaltechniques. Because the connections are established by free wires, nodifficulties arise from the need for the connections made outside of thesensing area to cross one another in places. In an alternative designthe connections made outside of the sensing area may be provided byconductive traces on the substrate similar to the electrodes forming thesensing area. This can be beneficial because the electrodes forming thesensing area and the electrical traces making the connections outside ofthe sensing area can be fabricated in single processing step.Conventional electrical jumpers can be used at the locations whereconnections outside of the sensing area cross one another. In yetanother alternative and more preferable design, the wiring isaccomplished by a combination of conductive traces on the substratesimilar to the electrodes forming the sensing area connecting someattachment nodes, plus a dielectric insulator deposited on top of theseconductors, plus conductive ink (e.g. silver ink) patterned on top ofthe dielectric insulator to connect together all remaining nodes needingto be joined. This produces a low cost, thin planar surface whichrequires only well-known processing steps, with no need for discretejumpers.

It will be appreciated that the numbers of rows and columns do not needto be 5 and 4 respectively as shown in FIG. 3; other numbers of rows andcolumns may be used to suit different geometries. Also, while the rowsand columns are shown to be of the same basic dimension giving rise tosquare cells 28, the rows and columns may be of non-matching or evennon-uniform dimensions giving rise to rectangular cells 28, or possiblyother shapes such as trapezoids. Furthermore, in cases where the regionsof the cells 28 are interleaved, they do not require angular patterns ofinterleaving as shown; the interleavings can be circular, spiral, orother shapes to accomplish the same general effect.

The position sensor 22 further comprises a series of capacitancemeasurement channels 42 coupled to respective ones of the rows of rowsensing electrodes and the columns of column sensing electrodes. Eachmeasurement channel is operable to generate a signal indicative of avalue of capacitance between the associated column or row of sensingelectrodes and a system ground. The capacitance measurement channels 42are shown in FIG. 3 as two separate banks with one bank coupled to therows of row sensing electrodes (measurement channels labeled y1 to y5)and one bank coupled to the columns of column sensing electrodes(measurement channels labeled x1 to x4). However, it will be appreciatedthat in practice all of the measurement channel circuitry will mostlikely be provided in a single unit such as a programmable orapplication specific integrated circuit. Furthermore, although nineseparate measurement channels are shown in FIG. 3, the capacitancemeasurement channels could equally be provided by a single capacitancemeasurement channel with appropriate multiplexing although this is not apreferred mode of operation. Equally the circuitry of the kind describedin U.S. Pat. No. 5,463,388 or similar can be used, which while using ascanning multiplexer does drive all the rows and columns with a singleoscillator simultaneously in order to propagate a laminar set of sensingfields through the overlying substrate. Preferably, the sensing channels42 are multiple in-phase charge-transfer sensors of the type describedin U.S. Pat. Nos. 5,730,165 or 6,466,036. Driving multiple ones of suchsensing circuits in a phase synchronous manner provides for a desirablelaminar field flow.

It is also noted that the substrate provides a valuable function infurther mixing the electric fields, so that not only are the fields fromX and Y lines better mixed above cells 28, but sensing gradients areproduced between adjacent ones of cells 28. This gives rise to theability to provide interpolated positions in both X and Y dimensionseven though the dimensions of cells 28 are wider than an actuatingobject. Thicker panels are noted to give better mixing performance andhence a better ability to interpolate position.

The signals indicative of the capacitance values measured by themeasurement channels 42 are provided to processing circuitry 44. Theprocessing circuitry is configured to determine the interpolatedposition of a capacitive load applied to the sensing area by an objectadjacent the position sensor. The interpolated position of thecapacitive load along the x-direction is determined from the signalsfrom the capacitance measurement channels associated with the columns ofcolumn sensing electrodes and the interpolated position of thecapacitive load along the y-direction is determined from the signalsfrom the capacitance measurement channels associated with the rows ofrow sensing electrodes. Once the position of the object along the x- andy-directions has been determined, the position is reported to a hostcontroller 46 so that it can take appropriate action.

FIG. 4 schematically shows in perspective view a device 50 including theposition sensor 22 shown in FIG. 3. The device in this example is ahand-held multimedia player comprising a housing 52 containing devicecontrol electronics (not shown) and a liquid crystal display screen 54.Various lines of text can be seen on the display screen, for example,representing a menu of commands for the device. The sensing area of theposition sensor overlays the display screen 54 with the electricalconnections between the various column and row sensing electrodes madeoutside of the sensing area being hidden from view within the housing52. The electrode layer is completely inside the housing, beingunderneath the cover plastic, being a film layer that is applied to theinterior of the enclosure. This provides for a control surface having noopenings and therefore no need for a bezel. The use of a single layer ofclear ITO with external node connections provides for high clarity andlow cost. A user can select from the menu of commands displayed on thescreen 54 by pointing at the appropriate location. The position sensorreports the location of the touch to the device controller which in turndetermines which command is to be executed. This is done by comparingthe position of the touch with the positions of the currently displayedmenu items.

Also shown in FIG. 4 is a finger 56 positioned at a point P adjacent theposition sensor 22 and above the display screen 54. The presence of thefinger 56 in the vicinity of the position sensor 22 affects thecapacitance of each of the rows and columns of sensing electrodesdifferently depending on the position of the finger within the sensingarea. Thus the processing circuitry 44 is able to determine the positionof the touch from the signals provided by the respective capacitancemeasurement channels.

FIGS. 5A and 5B are graphs schematically showing the signals generatedby the capacitance measurement channels 42 for the position sensor 22when the finger 56 is at the position shown in FIG. 4. FIG. 5A shows thesignals C_(x) from respective ones of the columns of column sensingelectrodes (x1 to x4). The vertical dotted lines schematically representthe boundaries of each of the columns. FIG. 5B shows the signals C_(y)from respective ones of the rows of row sensing electrodes (y1 to y5)with the vertical dotted lines representing the boundaries of each ofthe rows. The signals provided by the capacitance measurement channelshave been processed according to conventional techniques, e.g.background capacitance removal, touch threshold detection, normalizationand filtering have been performed as desired.

It can be seen from FIG. 5A that the presence of the finger 56 providesthe greatest increase in capacitive coupling to system ground for columnx2 (i.e. column x2 shows the greatest signal value). This means thepoint P corresponding to the interpolation or centroid of the capacitiveload applied by the finger 56 is within column x2. Furthermore, theincrease in capacitive coupling to system ground for column x3 isgreater than that for column x1. This means the point P is closer tocolumn x3 than it is to x1. The determination of the position of point Palong the x-direction is thus made by comparing the signals from thedifferent columns of column sensing electrodes, and in particular bydetermining the interpolation or centroid of the signal values. This canbe done using conventional processing techniques. In this case theinterpolation or centroid of the distribution of signals shown in FIG.5A is determined to be at position X_(P). Assuming the columns to be ofunit width, and taking the left hand boundary of column x1 to be x=0,point P is at a position along the x-direction of around x=1.8 units, asmarked in FIG. 5A by an arrow. A similar analysis is made for thesignals from the rows of row sensing electrodes. Assuming the rows to beof unit width, and taking the top most boundary of row y1 to be y=0,point P is at a position Y_(P) along the y-direction of around y=2.8units, again as marked an arrow. Thus the position P of the finger isdetermined to be at (x,y)=(1.8, 2.8). It is noted that the inherentinterpolation provided by the different capacitive couplings of thefinger to neighboring columns/rows means the centroid or interpolationof the capacitive load applied by the finger (i.e. the deemed positionof the touch) can be determined with a resolution that is better thanthe characteristic size of the sensing cells.

The reported XY position from position sensors according to someembodiments of the invention can be distorted depending on the size,placement and shape of the cells. However, this hardly has any neteffect in practical use for menu button usage or other forms of input,as the reported position can be readily corrected, for example via alookup table, or, the coordinates of menu buttons can be merelycompensated for any distortion. The XY distortion caused by the cellsize is repeatable from one unit to the next, as it is a physicalphenomenon linked to the pattern itself.

For example, FIG. 9 shows a keypad or touchscreen of the type of FIG. 3,having a 5×4 array of sensing cells 28, with a diagonal line 91 drawnacross the surface from top left to bottom right. The actual reportedposition may instead be as per solid line 93. The reported line 93 canbe readily corrected in X and Y using a correction algorithm or lookuptable so the final reported position is corrected to be properly alongideal line 91. Alternatively keys that are mapped into the sensitivearea of the position sensor 22 can be inverse-distorted to compensatefor the reported distortion as shown in FIG. 10. Here, physicallydesired key outlines 101 and 102 are distorted into reported shapes 103and 104. Rather than attempt to correct the reported X-Y data, the keyoutlines for purposes of key recognition can be distorted into the samereported outline shapes 103 and 104 as shown. If this is done, thereported keys are made identical to the desired shapes 101 and 102.

FIG. 6 schematically shows a plan view of the display screen 54 of thedevice 50 shown in FIG. 4 displaying a menu of commands. The menu ofcommands displayed to a user includes a series of box outlines in whichthe numbers 0 to 9 are displayed, a box outline containing the word“ENTER”, and a box outline of a box partially filled with shading andhaving gradations marked next to it representing the volume of musicbeing played as a fraction of maximum volume. Also shown on the display54 is a region bounded by a dotted line and showing some previouslyentered commands. The pattern of sensing electrodes associated with theposition sensor overlaying the display screen is also shown in FIG. 6,although it will be appreciated that the position sensor is transparentand would not be visible in practice. Since the sensing layer andassociated electronics is able to report an X-Y location, the positionof buttons is arbitrary as it would be with any analogue touch screeninput device. Thus, any known interface schema can be deployed over theface of the screen, such as menu buttons, sliders, wheels, gesturerecognition, character recognition, and the like. Furthermore theseschemes do not need to be aligned with the cells, and can be placedarbitrarily over the surface.

FIG. 7 schematically shows in plan view a two-dimensional capacitiveposition sensor 72 according to another embodiment of the invention.This position sensor again has five rows of sensing cells (labeled y1 toy5) but has only three columns of sensing cells (labeled x1 to x3).Column X2 forms a continuous spine 73 in the sensor area, andconnections 38 (similar to the correspondingly numbered connectionsshown in FIG. 3) are shown which connect the rows together externally tothe sensing area and connections 40, 41 (similar to the correspondinglynumbered connections shown in FIG. 3) make the outer columns continuousexternally to the sensing area. This position sensor has a total offifteen sensing cells. This means it will generally have less positionalresolution along the x-direction than the position sensor 22 shown inFIG. 3 if it were to have same size sensing area as that sensor.Alternatively, it may have the same (or better) positional resolution ifit has a smaller sensing area than the sensor shown in FIG. 3. Theoperation of the position sensor 72 shown in FIG. 7 is otherwise similarto and will be understood from the position sensor 22 of FIG. 3.

FIG. 8 schematically shows in plan view a two-dimensional capacitiveposition sensor 82 according to another embodiment of the invention.This position sensor has five rows and three columns of sensing cells. Afirst 84 and a second 86 sensing cell are identified by dotted outlines.In this example, the row and column sensing electrodes of each sensingcell do not spiral around one another. In sensing cells in column x2(e.g. sensing cell 84) the column sensing electrode runs continuouslythrough the sensing cell as a spine, with the row sensing electrodecomprising two conductive regions on either side of the column sensingelectrode. In sensing cells in columns at the edge of the sensing area(i.e. columns x1 and x3, e.g. sensing cell 86) the row sensing electroderuns continuously through the sensing cell with the column sensingelectrode comprising two conductive regions on either side of the rowsensing electrode. The operation of the position sensor 82 shown in FIG.8 is otherwise similar to and will be understood from the positionsensors 22, 72 of FIGS. 3 and 7. It will be understood the sensing cellsof FIG. 8 may also be considered to be interleaved, albeit in a minimalfashion. This shows that other basic shapes are also possible other thandiamonds or closely intertwined traces. The important aspect is that ina cell, there exists a portion of a row electrode and a portion of acolumn electrode.

The size of the sensing area in a given position sensor will depend onits implementation. For example in a hand-held mobile device of the kindshown in FIG. 4, a sensing area on the order of 4 cm (x-direction) by 5cm (y direction) might be suitable. This would provide sensing cells onthe order of 1 cm². This is comparable to the typical size of a fingertip and so can ensure there is good capacitive coupling to both the rowand column sensing electrodes within each cell when used to sense theposition of a user's finger. However, larger or smaller sensing areascould equally be employed. There is also no need for the columns androws to have the same widths, although if they were different it wouldmean the positional resolution might be different in the two directions.

Furthermore, there is no limit on the number of rows that may used whilestill providing for a sensing area having a single layer of sensingelectrodes within the sensing area (i.e. sensing electrodes on one sideof the substrate only). The patterns shown in FIGS. 3, 7 and 8 maysimply be repeated in y with corresponding additional capacitancemeasurement channels being provided for the additional rows of rowsensing electrodes. However, it is not possible to have both more thanfour rows and more than four columns for a position sensor havingsensing electrodes on one side of the substrate only.

It will also be understood that it is not necessary for the positionsensor to have a continuous spine within the sensing area to connectbetween column sensing electrodes in columns that are not at an edge ofthe sensing area. For example, the spines associated with columns x2 andx3 in FIG. 3 could be broken at some point along their length withconnections made outside of the sensing area between the respectivegroups of column sensing electrodes above and below the break. Forexample, the spines could be broken between rows y2 and y3 so that therow sensing electrodes in columns x1 and x2 of these rows can beconnected to the row sensing electrodes in columns x3 and x4 byconnections made within the sensing area through the break in thespines. There would then be no need for connections made outside of thesensing area for these rows, although connections outside of the sensingarea would be needed for columns x2 and x3.

It will be appreciated that position sensors embodying the invention mayincorporate a variety of additional features. For example, in someapplications it is desirable to have a ‘wakeup’ function, whereby theentire device ‘sleeps’ or is in some quiescent or background state. Insuch cases, it is often desirable to have a wake signal from mereproximity of a human body part some distance away. The element can bedriven as a single large capacitive electrode without regard to positionlocation, while the unit is in the background state. During this statethe electronic driver logic looks for a very small change in signal, notnecessarily enough to process as a 2D coordinate, but enough todetermine that an object or human is in proximity. The electronics then‘wakes up’ the overall system and the element is driven so as to becomea true position sensor once again.

Finally, it is noted that although the term “touch” is frequently usedin the above description, a position sensor of the kind described abovecan be sufficiently sensitive that it is able to register the locationof an adjacent finger (or other object such as a stylus) withoutrequiring physical contact. The term “touch” as used herein shouldtherefore be interpreted accordingly.

What is claimed is:
 1. A device comprising: a graphical display; asensing area-defined on a surface of a substrate that overlays thegraphical display, the graphical display being visible through thesensing area; and a plurality of sensing cells arranged in the sensingarea in a plurality of rows and columns, the sensing cells beingconfigured to sense a position of an object within the sensing area,each of the sensing cells comprising a row-sensing electrode and acolumn-sensing electrode, the row-sensing electrode of each of one ormore of the sensing cells being continuous with respect to therow-sensing electrode of each of one or more of the sensing cellsadjacent to it in its row, the column-sensing electrode of each of oneor more of the sensing cells being continuous with respect to thecolumn-sensing electrode of each of one or more of the sensing cellsadjacent to it in its column, the column-sensing electrode and therow-sensing electrode in each sensing cell being spirally interleavedwith one another; and a processor in communication with the plurality ofsensing cells and operable to correlate the position of the objectwithin the sensing area with a virtual button associated with thegraphical display.
 2. The sensor of claim 1, further comprising a columnwrap-around connection coupling a portion of the column-sensingelectrode located at opposing ends of the columns of the sensing cells,the column wrap-around connection provided along a periphery of thesensing area.
 3. The sensor of claim 1, further comprising a rowwrap-around connection coupled to a portion of the row-sensing electrodelocated at opposing ends of the rows of the sensing cells, the rowwrap-around connection comprises a conductive trace deposited on thesubstrate along a periphery of the sensing area.
 4. The sensor of claim3, further comprising a column wrap-around connection coupling a portionof the column-sensing electrode located at opposing ends of the columnsof the sensing cells, the column wrap-around connection provided along aperiphery of the sensing area.
 5. The sensor of claim 1, wherein one ormore of the row-sensing electrodes is continuous with respect to therow-sensing electrode of each of one or more of the sensing cellsadjacent to it in its row and its column-sensing electrode is alsocontinuous with respect to the column-sensing electrode of each of oneor more of the sensing cells adjacent to it in its column.
 6. The sensorof claim 1, further comprising a plurality of capacitance measurementchannels connected to respective ones of the row-sensing andcolumn-sensing electrodes, wherein each measurement channel is operableto generate a signal indicative of a capacitance between its associatedrow-sensing or column-sensing electrodes and a system ground.
 7. Thesensor of claim 1, wherein the sensing area is defined on a substratecomprising a transparent material.
 8. The sensor of claim 1, wherein therow-sensing and column-sensing electrodes comprise a transparentelectrically conductive material.
 9. A method comprising: displaying aplurality of virtual buttons on a graphical display; sensing a positionof an object within a sensing area defined on a surface of a substratethat overlays the graphical display, the graphical display being visiblethrough the sensing area, the sensing area comprising a plurality ofsensing cells arranged in a plurality of rows and columns, the sensingcells being configured to sense a position of an object within thesensing area, each of the sensing cells comprising a row-sensingelectrode and a column-sensing electrode, the row-sensing electrode ofeach of one or more of the sensing cells being continuous with respectto the row-sensing electrode of each of one or more of the sensing cellsadjacent to it in its row, the column-sensing electrode of each of oneor more of the sensing cells being continuous with respect to thecolumn-sensing electrode of each of one or more of the sensing cellsadjacent to it in its column, the column-sensing electrode and therow-sensing electrode in each sensing cell being spirally interleavedwith one another; communicating a plurality of signals resulting from acapacitance sensed by the row-sensing and column-sensing electrodes andindicative of the position of the object within the sensing area; andcorrelating the position of the object within the sensing area with aselected one of the plurality of virtual buttons displayed on thegraphical display.
 10. The method of claim 9, wherein the sensing areafurther comprises a column wrap-around connection coupling a portion ofthe column-sensing electrode located at opposing ends of the columns ofthe sensing cells, the column wrap-around connection provided along aperiphery of the sensing area.
 11. The method of claim 9, wherein thesensing area further comprises a row wrap-around connection coupled to aportion of the row-sensing electrode located at opposing ends of therows of the sensing cells, the row wrap-around connection comprises aconductive trace deposited on the substrate along a periphery of thesensing area.
 12. The method of claim 11, wherein the sensing areafurther comprises a column wrap-around connection coupling a portion ofthe column-sensing electrodes located at opposing ends of the columns,the column wrap-around connection provided-along a periphery of thesensing area.
 13. The method of claim 9, wherein one or more of therow-sensing electrodes of each of one or more of the sensing cells iscontinuous with respect to the row-sensing electrode of each of one ormore of the sensing cells adjacent to it in its row and itscolumn-sensing electrode is also continuous with respect to thecolumn-sensing electrode of each of one or more of the sensing cellsadjacent to it in its column.
 14. The method of claim 9, wherein thesubstrate comprises a transparent material.
 15. The method of claim 9,wherein row-sensing and column-sensing electrodes comprise a transparentelectrically conductive material.
 16. A computer-readable non-transitorystorage media embodying logic that is operable when executed to: displaya plurality of virtual buttons on a graphical display; sense a positionof an object within a sensing area defined on a surface of a substratethat overlays the graphical display, the sensing area comprising aplurality of sensing cells arranged in a plurality of rows and aplurality of columns, the sensing cells being configured to sense aposition of an object within the sensing area, each of the sensing cellscomprising a row-sensing electrode and a column-sensing electrode, therow-sensing electrode of each of one or more of the sensing cells beingcontinuous with respect to the row-sensing electrode of each of one ormore of the sensing cells adjacent to it in its row, the column-sensingelectrode of each of one or more of the sensing cells being continuouswith respect to the column-sensing electrode of each of one or more ofthe sensing cells adjacent to it in its column, the column-sensingelectrode and the row-sensing electrode in each sensing cell beingspirally interleaved with one another; communicate a plurality ofsignals resulting from a capacitance sensed by the row-sensing andcolumn-sensing electrodes indicative of the position of the objectwithin the sensing area; and correlate the position of the object withinthe sensing area with a selected one of the plurality of virtual buttonsdisplayed on the graphical display.
 17. The media of claim 16, furthercomprising a column wrap-around connection coupling a portion of thecolumn-sensing electrode located at opposing ends of the columns of thesensing cells, the column wrap-around connection provided along aperiphery of the sensing area.
 18. The media of claim 16, wherein thesensing area further comprises a row wrap-around connection coupled to aportion of the row-sensing electrode located at opposing ends of therows of the sensing cells, the row wrap-around connection comprises aconductive trace deposited on the substrate along a periphery of thesensing area.
 19. The media of claim 16, wherein one or more of therow-sensing electrodes of each of one or more of the sensing cells iscontinuous with respect to the row-sensing electrode of each of one ormore of the sensing cells adjacent to it in its row and itscolumn-sensing electrode is also continuous with respect to thecolumn-sensing electrode of each of one or more of the sensing cellsadjacent to it in its column.
 20. The media of claim 16, wherein thesubstrate comprises a transparent material.
 21. The media of claim 16,wherein the row-sensing and column-sensing electrodes comprise atransparent electrically conductive material.